This invention relates to displays having improved contrast.
The contrast ratio of displays is diminished by ambient light reflecting from the surfaces of the display. This effect occurs for all types of displays--backlit, reflective, or projection displays--and regardless of whether the display image is passive (i.e., relies of extrinsic lighting for visualization, for example a liquid crystal display) or self-luminous (e.g., a cathode ray tube display). To improve contrast, it is desirable to reduce or eliminate ambient reflections, preferably without decreasing significantly the brightness of the display image.
One approach to this problem in the case of backlit or rear projection displays is to add a contrast enhancing filter to the faceplate of the display. The filter attenuates ambient light more than light from the image, because ambient light must pass through the filter twice, while the image light does so only once. For example, if the filter attenuates light passing therethrough by a factor of 3.2, it will reduce ambient light reflections by a factor of 3.2 squared, or ten, while the image brightness will be reduced by a factor of only 3.2. However, the increased contrast is achieved at the expense of image brightness, because the image is now also significantly less bright than it would have been without the filter's presence.
For the aforementioned reasons, it is desirable to provide a display in which ambient light reflections are reduced, by a factor of preferably about 10, while the image brightness remains undiminished. The present invention provides displays having such characteristics.